U.S. patent application number 11/480193 was filed with the patent office on 2008-01-03 for fuel cell/combustor systems and methods for aircraft and other applications.
This patent application is currently assigned to The Boeing Company. Invention is credited to David L. Daggett.
Application Number | 20080001038 11/480193 |
Document ID | / |
Family ID | 38875599 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080001038 |
Kind Code |
A1 |
Daggett; David L. |
January 3, 2008 |
Fuel cell/combustor systems and methods for aircraft and other
applications
Abstract
Fuel cell/combustor systems and methods for aircraft and other
applications are disclosed. A system in accordance with one
embodiment includes a fuel cell having an outlet positioned to
remove output products from the fuel cell. The system can further
include a fuel supply carrying a fuel having a different
composition than the output products (e.g., aviation fuel), and a
combustion chamber. The combustion chamber can in turn include a
first inlet coupled to the outlet of the fuel cell to receive
output products from the fuel cell, and a second inlet coupled to
the fuel supply to receive the fuel. At least one combustion zone
can be positioned in fluid communication with the first and second
inlets to burn both the output products and the fuel.
Inventors: |
Daggett; David L.;
(Snohomish, WA) |
Correspondence
Address: |
PERKINS COIE, LLP
P.O. BOX 1247, PATENT - SEA
SEATT;E
WA
98111-1247
US
|
Assignee: |
The Boeing Company
Chicago
IL
|
Family ID: |
38875599 |
Appl. No.: |
11/480193 |
Filed: |
June 29, 2006 |
Current U.S.
Class: |
244/53R |
Current CPC
Class: |
B64D 27/02 20130101;
F23C 2900/03002 20130101; B64D 2041/005 20130101; Y02T 90/36
20130101; Y02T 90/40 20130101; F23C 2900/9901 20130101 |
Class at
Publication: |
244/53.R |
International
Class: |
B64D 33/00 20060101
B64D033/00; B64D 29/00 20060101 B64D029/00 |
Claims
1. An aircraft power generation system, comprising: a reformer
coupleable to an aircraft fuel supply to receive aviation fuel; a
fuel cell coupled to the reformer to receive reformed fuel, the
fuel cell having an outlet positioned to remove output products
from the fuel cell; and a combustion chamber that includes: a first
inlet coupled to the outlet of the fuel cell to receive the output
products from the fuel cell; a second inlet coupleable to the
aircraft fuel supply to receive aviation fuel; and at least one
combustion zone coupled to the first and second inlets, the at
least one combustion zone being positioned to burn the output
products and the aviation fuel.
2. The system of claim 1 wherein the combustion chamber is part of
an airbreathing, turbofan engine configured to provide primary
propulsive power to an aircraft.
3. The system of claim 2, further comprising a controller
operatively coupled to the engine, and wherein the controller is
programmed with instructions to: provide the output products to the
first inlet at engine settings including engine idle; and provide
the aircraft fuel to the second inlet only at engine settings above
engine idle.
4. The system of claim 2 wherein the turbofan engine includes a
compressor, but does not include an engine generator driven by the
compressor.
5. The system of claim 1 wherein the at least one combustion zone
includes a first combustion zone coupled to the first inlet and a
second combustion zone coupled to the second inlet, and wherein the
first combustion zone is positioned in third communication with the
second combustion zone to provide a pilot flame for combustion in
the second combustion zone.
6. The system of claim 1 wherein the first combustion zone is
positioned annularly outwardly from the second combustion zone.
7. The system of claim 1 wherein the combustion chamber includes a
lean premix, prevaporized, low NO.sub.x combustion chamber.
8. The system of claim 1 wherein the fuel cell is coupled to an
electrical device to power the electrical device, and wherein the
system further comprises: an aircraft fuselage; a wing carried by
the fuselage, the wing housing the aircraft fuel supply; and an
engine housing the combustion chamber.
9. The system of claim 1 wherein the fuel cell is one of a
plurality of solid oxide fuel cells, each having an electrical
output terminal coupled to an electrical output terminal of another
fuel cell.
10. The system of claim 1 wherein the reformer is configured to
reform aviation fuel to hydrogen and carbon monoxide.
11. The system of claim 1 wherein the fuel cell is configured to
emit the output products at a temperature of at least 800.degree.
C.
12. The system of claim 1 wherein the reformer is sized to provide
to the fuel cell reformed fuel at a rate higher than a rate at
which the fuel cell converts the reformed fuel to electrical
energy.
13. The system of claim 1 wherein: the combustion chamber is part
of an airbreathing, turbofan engine configured to provide primary
propulsive power to an aircraft; the at least one combustion zone
includes a first combustion zone coupled to the first inlet and a
second combustion zone coupled to the second inlet, and wherein the
first combustion zone is positioned to burn hydrogen and provide a
pilot flame for combustion of Jet A fuel in the second combustion
zone; and wherein the system further comprises: a controller
operatively coupled to the engine, and wherein the controller is
programmed with instructions to: provide the output products to the
first inlet at engine settings including engine idle; and provide
the aircraft fuel to the second inlet only at engine settings above
engine idle.
14. The system of claim 1 wherein the outlet of the fuel cell is
co-located with the first inlet of the combustion chamber.
15. A power generation system, comprising: a fuel cell having an
outlet positioned to remove output products from the fuel cell; a
fuel supply carrying a fuel having a different composition than the
output products; and a combustion chamber that includes: a first
inlet coupled to the outlet of the fuel cell to receive output
products from the fuel cell; a second inlet coupled to the fuel
supply to receive the fuel; and at least one combustion zone in
fluid communication with the first and second inlets, the at least
one combustion zone being positioned to burn the output products
and the fuel.
16. The system of claim 15 wherein the fuel supply carries aviation
fuel.
17. The system of claim 15 wherein the fuel supply carries diesel
fuel.
18. The system of claim 15 wherein the fuel supply includes an
aircraft wing tank, and wherein the combustion chamber is part of
an airbreathing, turbofan engine configured to provide primary
propulsive power to an aircraft.
19. A method for generating power aboard an aircraft, comprising:
reforming a first portion of aviation fuel onboard the aircraft to
form a reformed fuel; generating electrical power for the aircraft
by passing the reformed fuel through a fuel cell; removing unspent
reformed fuel from the fuel cell; and generating propulsive power
for the aircraft by combusting the unspent reformed fuel and a
second portion of the aviation fuel in a combustion chamber.
20. The method of claim 19 wherein combusting the unspent reformed
fuel includes combusting reformed fuel, which has not been
converted to electrical energy, in a pilot flame positioned to
stabilize combustion of the second portion of the aviation
fuel.
21. The method of claim 19 wherein removing unspent reformed fuel
includes removing unspent reformed fuel at a temperature above an
autoignition temperature of the aircraft fuel, and wherein the
method further comprises providing the unspent reformed fuel to the
combustor at a temperature above the autoignition temperature of
the aircraft fuel.
22. The method of claim 19, further comprising providing reformed
fuel to the fuel cell at a rate higher than a rate at which the
fuel cell electrochemically converts reformed fuel to electrical
energy.
23. The method of claim 19 wherein removing unspent reformed fuel
from the fuel cell includes removing unspent reformed fuel having a
temperature of at least 800.degree. C.
24. The method of claim 19 wherein the aviation fuel includes Jet A
fuel, and wherein reforming a first portion of the aviation fuel
includes forming hydrogen and carbon monoxide.
25. The method of claim 19, further comprising providing air that
is heated and compressed by a compressor of a turbofan engine to
the fuel cell, and providing output products of the fuel cell to a
turbine of the turbofan engine, via the combustion chamber.
Description
TECHNICAL FIELD
[0001] The present disclosure is directed to fuel cells/combustor
systems and methods, which may be applied to aircraft and/or other
devices or installations.
BACKGROUND
[0002] Aircraft manufacturers are under constant pressure to
improve the fuel efficiency of modern commercial transport
aircraft. Improved fuel efficiency can increase the range of the
aircraft, reduce CO.sub.2 emissions and/or reduce the cost of
operating the aircraft. While modern, high-bypass turbofan engines
have shown significant improvements in fuel efficiency when
compared with the turbojet engines developed at the beginning of
the jet age, aircraft manufacturers must continually strive to
improve aircraft and aircraft engine performance in response to
customer demands.
[0003] One relatively recent development in modern commercial
aircraft includes replacing hydraulic and/or pneumatic aircraft
actuators with electrically powered actuators. These actuators may
be used to power a myriad of aircraft systems, including flaps,
ailerons, and rudders. Electrically powered actuators use power
provided by generators that are in turn driven by the aircraft
turbofan engines (which also provide the main propulsive force for
the aircraft). While this technology evolution has proven
beneficial, it increases the power demands placed on aircraft
engine generators, which typically requires an increase to the size
of the generators. Furthermore, current aircraft engine generators
are typically less than 45% efficient at converting Jet-A aviation
fuel into electrical power during cruise operations. Accordingly,
there is a strong desire to improve the efficiency with which
electrical power is generated on board the aircraft, so as to keep
the engine size as low as possible, reduce the amount of fuel
carried aboard the aircraft, and/or improve the overall efficiency
and environmental performance of the aircraft.
[0004] One approach to improving the efficiency with which
electrical energy is generated onboard the aircraft is to use
electrochemical fuel cells. For example, fuel cells have been
identified as a replacement for the aircraft auxiliary power unit.
However, fuel cells tend to be heavy, in many instances due to the
peripheral equipment (e.g., compressors) used to provide air to the
fuel cells for operation.
[0005] Another pressure that aircraft manufacturers face is
reducing the emissions of potentially harmful gases present in the
exhaust stream from the turbofan engines. Such emissions typically
include NO.sub.x emissions, which can pollute the air near
airports, and can lead to the formation of ozone at cruise
altitudes. In response to pressures to reduce the emissions of such
gases, low NO.sub.x combustors have been developed. These
combustors typically operate at lower peak temperatures than more
conventional combustors, by using a fuel-lean mixture, and by
significantly increasing the degree to which the fuel is mixed with
air before being combusted. However, a potential drawback with this
arrangement is that the lean mixture may produce an unstable flame.
As a result, the flame may be more likely to blow out ("flameout"),
which can produce an unplanned unstart of the aircraft engine. One
approach to addressing this drawback is to provide the combustor
with a small fuel-rich spray at each nozzle. However, burning such
a spray tends to produce the very emissions that the low NO.sub.x
combustor is intended to reduce. In light of the foregoing, there
is a desire to both improve the overall fuel efficiency and
robustness of aircraft engines and reduce the emissions of
potentially harmful exhaust products.
SUMMARY
[0006] The present summary is provided for the benefit of the
reader only, and is not intended to limit in any way the scope of
the invention as set forth by the claims. An aircraft power
generation system in accordance with one aspect of the invention
includes a fuel reformer that is coupleable to an aircraft fuel
supply to receive aviation fuel. A fuel cell can be coupled to the
reformer to receive reformed fuel (e.g., hydrogen and/or carbon
monoxide). The fuel cell further includes an outlet positioned to
remove output products from the fuel cell. The system can further
include a combustion chamber that in turn includes a first inlet
coupled to the outlet of the fuel cell to receive the output
products from the fuel cell. A second inlet of the combustion
chamber can be coupleable to the aircraft fuel supply to receive
aviation fuel. The combustion chamber can further include at least
one combustion zone coupled to the first and second inlets and
positioned to burn both the output products and the aviation fuel.
Accordingly, the fuel cell can provide electrical power for the
aircraft, and the combustion chamber can provide propulsive power
for the aircraft.
[0007] In particular aspects, the combustion zone includes a first
combustion zone coupled to the first inlet and a second combustion
zone coupled to the second inlet. The first combustion zone can be
positioned to provide a pilot flame for combustion in the second
combustion zone. Accordingly, the output products received from the
fuel cell can be burned in a manner that stabilizes the flame for
combustion of the aviation fuel.
[0008] In still a further aspect, the reformer is sized to provide
to the fuel cell reformed fuel at a higher rate than the rate at
which the fuel cell converts the reformed fuel to electrical
energy. As a result, the output products can include unspent
reformed fuel (e.g., hydrogen and/or carbon monoxide) which can
burn readily in the combustion chamber to provide a stable
flame.
[0009] In other aspects, the power generation system need not be
installed on an aircraft. Accordingly, a power generation system in
accordance with another aspect includes a fuel cell having an
outlet positioned to remove output products from the fuel cell, a
fuel supply carrying a fuel having a different composition than
that of the output products, and a combustion chamber. The
combustion chamber can in turn include a first inlet coupled to the
output of the fuel cell to receive output products from the fuel
cell, and a second inlet coupled to the fuel supply to receive the
fuel. The combustion chamber can further include at least one
combustion zone in fluid communication with the first and second
inlets, the combustion zone being positioned to burn the output
products and the fuel.
[0010] Still another aspect is directed to a method for generating
power aboard an aircraft. For example, the method can include
reforming a first portion of aviation fuel on board the aircraft to
form a reformed fuel, and generating electrical power for the
aircraft by passing the reformed fuel through a fuel cell. The
method can further include removing unspent reformed fuel from the
fuel cell, and generating propulsive power for the aircraft by
combusting the unspent reformed fuel and a second portion of the
aviation fuel in a combustion chamber. For example, combusting the
unspent reformed fuel can include combusting the unspent reformed
fuel in a pilot flame that is positioned to stabilize combustion of
the second portion of the aviation fuel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a partially schematic illustration of an aircraft
having a power generation system configured in accordance with an
embodiment of the invention.
[0012] FIG. 2 is a partially schematic illustration of a turbofan
engine suitable for powering an aircraft such as the one shown in
FIG. 1.
[0013] FIG. 3 is a schematic block diagram illustrating the
production of energy in a portion of a power generation system in
accordance with an embodiment of the invention.
[0014] FIG. 4 is a partially schematic, cross-sectional
illustration of a combustor that includes a fuel cell in accordance
with an embodiment of the invention.
[0015] FIG. 5 is a partially schematic illustration of a fuel cell
device that includes multiple fuel cells in accordance with an
embodiment of the invention.
DETAILED DESCRIPTION
[0016] The present disclosure describes power generation systems
and methods, including fuel cell/combustor systems and methods for
aircraft and other applications. Certain specific details are set
forth in the following description and in FIGS. 1-5 to provide a
thorough understanding of various embodiments of the invention.
Well-known structures, systems and methods often associated with
such systems have not been shown or described in detail to avoid
unnecessarily obscuring the description of the various embodiments
of the invention. In addition, those of ordinary skill in the
relevant art will understand that additional embodiments of the
invention may be practiced without several of the details described
below.
[0017] FIG. 1 is a partially schematic illustration of an aircraft
100 that includes a power generation system 110 configured in
accordance with an embodiment of the invention. The aircraft 100
can include a fuselage 101, wings 102 and multiple fuel tanks 103
that carry aviation fuel (e.g., Jet-A fuel). The fuel tanks 103 can
be housed in the wings 102 and/or the fuselage 101. The power
generation system 110 can include a propulsion system 111 as well
as other power systems, for example, an auxiliary power unit (APU)
114 housed in an empennage 104 of the aircraft 100. The propulsion
system 111 can include a turbofan engine 112 housed in a nacelle
113. In an embodiment shown in FIG. 1, the aircraft 100 includes
two turbofan engines 112, each carried by one of the wings 102. In
other embodiments, the aircraft 100 can include other engine
arrangements.
[0018] FIG. 2 is a schematic illustration of an embodiment of the
turbofan engine 112. The engine 112 includes a compressor 115 that
receives core air 116 provided by an inlet in the nacelle 113. The
compressor 115 pressurizes the core air 116 and provides it to a
combustor 130. In the combustor 130, the compressed core air 116 is
mixed with fuel 117 and burned. A fuel cell 133 can operate in
conjunction with the combustion process in the combustor 130 to
improve the overall performance of the turbofan engine 112, as will
be discussed in greater detail later with reference to FIGS.
3-5.
[0019] The combustion products produced by the combustor 130 are
provided to a high pressure turbine 118, which drives the
compressor 115. The combustion products are then further expanded
through a low pressure turbine 119 which drives a fan 120. The fan
propels bypass air 121 around the core of the engine 112. The
bypass air 121 mixes with exhaust gas 122 exiting the low pressure
turbine 119 to provide forward thrust.
[0020] The operation of various components of the engine 112, in
particular the delivery of fuel to the combustor 130 and the fuel
cell 133 can be controlled by a controller 150. Accordingly, the
controller 150 can include a computer and/or computer-readable
medium containing instructions that direct the operation of the
engine 112. The controller 150 therefore automates or at least
partially automates many of the processes carried out by the engine
112.
[0021] FIG. 3 is a block diagram illustrating the processes carried
out by the combustor 130 and the fuel cell 133 initially described
above with reference to FIG. 2. As shown in FIG. 2, a portion of
the fuel 117 carried aboard the aircraft is provided to a reformer
131. The reformer 131 can be configured to transform a hydrocarbon
fuel (e.g., Jet-A aviation fuel) into a reformed fuel having
constituents that are compatible with an electrochemical fuel cell.
Such constituents can include hydrogen and/or carbon monoxide. The
reformed fuel 132, along with a portion of the core air 116, is
then provided to the fuel cell 133. An electrochemical reaction
takes place in the fuel cell 133 to produce electrical energy 134
and output products 135.
[0022] In a particular embodiment, the fuel cell 133 includes a
solid oxide fuel cell (SOFC) that produces high temperature output
products 135, including unspent fuel (e.g., a portion of the
reformed fuel 132). For example, the output products 135 may
include hydrogen and carbon monoxide at a temperature of at least
800.degree. C. In particular embodiments, the temperature of the
output products 135 can be from about 800.degree. C. to about
1,000.degree. C. The output products 135 are provided to a
combustion chamber 136, which also receives a portion of the fuel
117 and the core air 116. The fuel received in the combustion
chamber 136, as well as the output products 135 received from the
fuel cell 133, are burned in the combustion chamber 136 to produce
propulsion energy 137. The propulsion energy 137 is harnessed
through the turbines 118, 119 (FIG. 2) as well as via direct jet
thrust. The electrical energy 134 produced by the fuel cell is used
to power electrically driven components of the aircraft (e.g.,
environmental control systems and/or other systems).
[0023] FIG. 4 is a partially schematic cross-sectional illustration
of an embodiment of the combustor 130. In this particular
embodiment, many of the components described above with reference
to FIG. 3 are housed within the combustor 130 itself. In other
embodiments, these components may be distributed outside the
combustor 130, without affecting the overall function of the
components. Housing at least some of these components within the
combustor 130 provides for a compact arrangement that can reduce
temperature and energy losses between the components.
[0024] The combustor 130 includes a fuel injector 138 that receives
the fuel 117 and directs one portion of the fuel 117 into the fuel
reformer 131, and directs another portion into a fuel/air premixer
143. The fuel 117 provided to the fuel reformer 131 and the
premixer 143 can be metered by valves 127 under the direction of
the controller 150. The fuel provided to the fuel reformer 131 is
converted in the reformer 131 to a reformed fuel and is passed
through the fuel cell 133 to produce the electrical energy 134.
Core air 116 is also provided to the fuel reformer 131 and the fuel
cell 133 to facilitate the reformation and energy generation
processes, respectively. The output products from the fuel cell 133
exit at a fuel cell outlet 139 and are received in a first inlet
140a of a combustion chamber 142. The fuel cell outlet 139 and the
first inlet 140a can be co-located so as to reduce or eliminate
pressure and temperature losses between the fuel cell 133 and the
combustion chamber 142. A first combustion zone 141a is positioned
at the first inlet 140a, and can include an optional first flame
holder 146a, shown schematically in FIG. 4. In other embodiments,
the first flame holder 146a can be eliminated, and the fuel cell
outlet 139 can operate as a flame holder. In either embodiment,
output products received from the fuel cell 133 are burned in the
first combustion zone 141a.
[0025] The combustion chamber 142 can further include a second
inlet 140b that receives the fuel/air mixture from the fuel/air
premixer 143. In a particular embodiment, the combustion chamber
142 can be a lean premix, prevaporized (LPP) low NO.sub.x
combustion chamber that receives a fuel-lean mixture. An optional
second flame holder 146b (shown schematically in FIG. 4) may be
provided in a second combustion zone 141b. The first and second
combustion zones 141a, 141b can have an annular arrangement, with
the first combustion zone 140a positioned annularly outwardly from
the second combustion zone 141b. Exhaust products from both
combustion zones can be directed through turbine inlet guide vanes
144 to the high pressure turbine 118.
[0026] In a particular embodiment, the combustion process taking
place in the first combustion zone 141a can stabilize the
combustion process taking place in the second combustion zone 141b.
For example, the output products received from the fuel cell 133
can include unspent reformed fuel including hydrogen. This
hydrogen-rich gas tends to burn very well and stably under a wide
range of combustor operating conditions. Accordingly, the burning
output products can provide a pilot flame that stabilizes
combustion of the un-reformed aviation fuel that is burned in the
second combustion zone 141b. In a further particular aspect of this
embodiment, the output products burned in the first combustion zone
141a are provided to the first combustion zone 141a at a
temperature above the autoignition temperature of these products
(e.g., in the range of from about 800.degree. C. to about
1000.degree. C. for a hydrogen-rich gas). Accordingly, when they
mix with air or another oxygen source, they autoignite. This
arrangement provides for additional robustness because the process
does not rely on an igniter for sustained operation. Nevertheless,
in some embodiments, an igniter may be used to initiate ignition if
the output products are initially below the autoignition
temperature, for example, during engine start-up.
[0027] The stable flame produced in the first combustion zone 141a
can reduce or eliminate adverse impacts that may be created by a
flameout in the second combustion zone 141b. In particular, because
a fuel-lean mixture is burned in the second combustion zone 141b,
the combustion process in this region may be susceptible to
flameout. With the presence of the robust, stable flame provided by
the combustion of the output products in the first combustion zone
141a, the likelihood for such flameouts can be reduced or
eliminated.
[0028] In a particular aspect of an embodiment shown in FIG. 4, the
controller 150 controls the interaction between the processes
taking place in the first combustion zone 141a and the second
combustion zone 141b. For example, the controller 150 can control
the rate at which fuel is provided to the fuel reformer 131 and the
fuel cell 133. By directing more fuel into the fuel reformer 131
and the fuel cell 133 than the fuel cell 133 can convert to
electrical energy 134, the output products can be made to include a
sufficient quantity of heated, but unburned or unspent reformed
fuel. As discussed above, the heated, unspent reformed fuel can
provide the basis for the combustion process in the first
combustion zone 141a.
[0029] The controller 150 can also control the amount of fuel
provided to the second combustion zone 141b. In a particular
embodiment, the fuel provided to the second combustion zone 141b
can be halted at all conditions other than engine idle.
Accordingly, at engine idle, the only combustion process in the
combustor 130 is the one that occurs in the first combustion zone
141a, with the flame provided there operating as a pilot flame. At
thrust conditions above engine idle, fuel can be provided to the
second combustion zone 141b and burned in a combustion process that
is stabilized by the pilot flame in the first combustion zone 141a
to produce the desired level of thrust.
[0030] In some instances, the fuel cell 133 shown in FIGS. 3 and 4
can be a single fuel cell. In other arrangements, such as one shown
in FIG. 5, a fuel cell device 145 includes a composite of
individual fuel cells 133 that are connected together and arranged
in a synergistic manner. Accordingly, the term fuel cell as used
herein includes one or more fuel cells. The fuel cells 133 can
include tubular, solid oxide fuel cells, prototypes of which have
been developed by (and/or are in development by) Siemens of Berlin,
Germany, Rolls Royce of Chantilly, Va., General Electric of Lynn,
Mass., and NanoDynamics of Buffalo, N.Y. These fuel cells 133 have
a hollow center through which the reformed fuel is passed, while
oxygen (e.g., the core air 116) passes around the outside of the
tube. A relatively low output voltage (e.g., 0.7 volts) is produced
between an anode 129 and a cathode 128. Accordingly, multiple fuel
cells 133 are coupled together to provide a useable electrical
power output. As shown in FIG. 5, the individual fuel cells 133 can
be coupled together in series to produce the output electrical
energy 134. In a particular aspect, a sufficient number of fuel
cells 133 can be provided in the fuel cell device 145 to produce
many kilowatts (e.g., approximately 250 kW) of electrical power for
each turbofan engine in which the device is incorporated. This
level of power can be sufficient to eliminate the need for a
separate electrical generator powered by the turbofan engine
(although the engine may still include backup generators powered by
the engine). In other embodiments, the power provided by the fuel
cells 133 can be sufficient to eliminate the need for other power
generators.
[0031] In another aspect of an arrangement shown in FIG. 5, the
individual fuel cells 133 are arranged in parallel in a fluid
dynamic sense, although they are connected in series in an
electrical sense. Accordingly, fuel 117 can be provided to multiple
fuel cells 133 at a common input manifold 147, and the output
products 135 can be received at a common output manifold 148. The
core air 116 can be circulated through the fuel cells 133 for use
during the electrochemical process that produces the electrical
energy 134.
[0032] One feature of several embodiments described above with
reference to FIGS. 1-5 is that they include a combustor that burns
two different types of fuel, e.g., the output products from a fuel
cell, and the unreformed aviation fuel. During many phases of
operation (e.g., at thrust settings above engine idle), both types
of fuel are burned simultaneously. One advantage of this
arrangement, as discussed above, is that the output products from
the fuel cell can be burned in a way that provides a pilot flame or
other stabilizing influence on the combustion process for the
aviation fuel. This feature can be particularly important for lean
premixed, prevaporized combustors, but can also have application to
other combustion processes. In any of these applications, the more
stable combustion processes provides for greater reliability of the
engine.
[0033] Another feature of several of embodiments described above is
that they include a fuel cell that is integrated into a turbofan
engine. One advantage of the arrangement is that the fuel cell can
readily use compressed air from the engine compressor, and can
provide exhaust products to the engine turbine. As a result, the
fuel cell need not have associated with it a separate compressor or
turbine, which would add weight to the aircraft. Also, the air from
the engine compressor is heated as a result of the compression
process, which reduces or eliminates the need to have a separate
heater or heat exchanger for the fuel cell 133.
[0034] Still another feature of several of the embodiments
described above is that the fuel cell can be integrated with the
turbofan engine in a manner that reduces the amount of redesign
work necessary to support the configuration. For example, some
existing combustor designs include a dual annular combustor
arrangement. This arrangement can readily support the addition of
the pilot flame combustion process described above.
[0035] Still another advantage of at least some of the foregoing
features is that the energy produced by the fuel cell can replace
one or more existing engine generator, and can provide electrical
energy at a higher efficiency than that of an existing engine
generator. Accordingly, several of the embodiments described above
result in a power system having lower energy consumption, lower
NO.sub.x emissions, and greater combustion stability than existing
arrangements.
[0036] From the foregoing, it will be appreciated that specific
embodiments of the invention have been described herein for
purposes of illustration, but that various modifications may be
made without deviating from the invention. For example, while
aspects of the invention have been described in the context of
aircraft turbofan engines, many of these aspects may also be
implemented in other power generation devices. In particular
examples, fuels other than aviation fuels (e.g., diesel fuel) and
output products from a fuel cell may be burned in a combustor that
is housed in an automobile, a truck, a land- or sea-based power
generator, and/or other applications. The fuel cells can carry out
electrochemical processes that produce useable output gases other
than hydrogen and/or carbon monoxide. While solid oxide fuel cells
are described above in the context of several embodiments, the fuel
cells can be of other types in other embodiments. Aspects of the
invention described in the context particular embodiments may be
combined or eliminated in other embodiments. For example, the
multiple fuel cell arrangement shown in FIG. 5 may be included in
any of the systems shown in FIGS. 1-4. Further, while advantages
associated with certain embodiments of the invention have been
described in the context of those embodiments, other embodiments
may also exhibit such advantages, and not all embodiments need
necessarily exhibit such advantages to fall within the scope of the
invention. Accordingly, the invention is not limited except as by
the appended claims.
* * * * *